The present invention relates generally to gear-type pumps and motors, and more specifically to reversible spur gear pumps or motors capable of operating under high pressure conditions.
Reversible gear pumps or motors of the type described include intermeshed spur gears rotatably mounted in a housing between a low pressure port and a high pressure port. Pressure plates are often provided in the housing at the ends of the gears. These plates include two circular portions having shaft receiving holes therethrough to define a figure-eight configuration. The purpose of the pressure plates is to confine the liquid in the gear chamber and improve the efficiency of the pump.
When in operation, the pressure differential existing between the low pressure and the high pressure sides of such a pump or motor places an unbalanced loading on the gears which can lead to wear, decreased efficiency and eventual failure. Under high pressure conditions, the unbalanced loading forces the gears against the inner surfaces of the housing at the low pressure side of the pump or motor. The surfaces of the housing are rapidly worn away by the pressure contact of the rotating gear teeth and the operating efficiency of the pump or motor is diminished until it eventually fails. High pressure deflection of the gear sets and shafts also produces severe bearing wear which in turn contributes to the movement of the gears against the housing wall at the low pressure side and aggravation of the wear problem.
Various attempts have been made in the past to counterbalance the high pressure loading on the gears of reversible pumps. Some of these proposals entailed a complicated and expensive housing construction having drilled or cored passageways, relief areas in the housing wall, etc. In many instances the construction has been such as to permit high pressure liquid to leak around the gears to the low pressure side of the pump or motor so as to diminish its operating efficiency. Another problem of certain prior art structures was the creation of high pressure hydraulic loading on the top and bottom of the gear set. The hydraulic loading acted to force the gears together and load the bearings, thereby producing severe bearing wear. Still another problem of some prior art constructions was that cavitation could occur on the faces of the pressure plates with the result that the plates were eroded or pitted.
A commercially successful, non-reversible gear pump capable of high pressure operation is disclosed in U.S. Pat. No. 4,087,216. The pump of that patent includes a pair of flow diverter plates that are effective to reduce severe unbalanced pressure loading on the gears. In a preferred embodiment of the diverter plate, a cavity or recess is formed in the outer peripheral edge of each circular plate portion. The two recesses are located on the same side of the centerline extending diametrically through the shaft receiving holes of the circular portions. A channel or the like is formed in the outer peripheral edge of each circular portion between the sides of the plate so as to extend from the recess therein to a terminating location on the other side of the centerline. The diverter plates are fitted into the pump housing so that the recesses are on the low pressure side of the pump or motor and the channels terminate on the high pressure side. During operation, the high pressure fluid is communicated through the channels to the low pressure side. The fluid pressure acts as a counterforce to at least partially balance the high pressure side loading and push the gears back towards a centered position. This allows the gears to function properly while minimizing bearing levels.
Operation of non-reversible pumps provided with diverter plates as described in U.S. Pat. No. 4,087,216 has shown that the diverter plate construction materially reduces bearing failure and wear of the pump housing. Such pumps have been operated at pressures up to 5,000 p.s.i. or higher for extended periods of time compared to the relatively short life of conventional gear pumps under the same operating conditions.